Channel identification in a MIMO telecommunications system

ABSTRACT

A channel identification system and method are provided to automatically identify ports of a base station (e.g., an eNodeB) to route downlink signals to appropriate access points in a telecommunication system. Primary and secondary synchronization signals may be identified in the downlink signals transmitted by the base station. A broadcast channel may be decoded for a downlink signal including the primary and secondary synchronization signals. Signal information may be used to extract a first cell-specific reference signal and generate a second cell-specific reference signal corresponding to one or more ports of the base station. The first and second cell-specific reference signals may be correlated to verify the identity of the channel corresponding to the ports of the base station.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional applicationSer. No. 15/549,057, titled “CHANNEL IDENTIFICATION IN A MIMOTELECOMMUNICATIONS SYSTEM” and filed Aug. 4, 2017, which is a U.S.National Stage application of PCT Application Serial No.PCT/US2016/014821, filed Jan. 26, 2016, and titled “CHANNELIDENTIFICATION IN A MIMO TELECOMMUNICATION SYSTEM,” which claims thebenefit of U.S. Provisional Application Ser. No. 62/114,658, filed Feb.11, 2015, and titled “Channel Identification in a MIMOTelecommunications System,” the contents of all of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to telecommunications, and,more particularly (although not necessarily exclusively), tomulti-input, multi-output (“MIMO”) channel identification in atelecommunication system.

BACKGROUND

A telecommunication system may include a distributed antenna system(“DAS”) or a repeater that may be used to extend the coverage of acellular communication system. For example, a DAS may extend coverage toareas of traditionally low signal coverage within buildings, tunnels, orin areas obstructed by terrain features. The telecommunication systemmay be communicatively coupled to one or more base stations, including,but not limited to, an eNodeB (“eNB”), that is compliant with a LongTerm Evolution (“LTE”) standard.

A DAS, for example, may include one or more head-end units (e.g., masterunits) that are communicatively coupled to the base stations. Thehead-end units may be coupled to ports of the base stations to formchannels between the head-end units and the respective base stationports. The DAS may also include multiple access points or remote unitsthat are communicatively coupled to a base station via a head-end unit.The remote units, each of which may include one or more transceivers andantennas, may be distributed across a coverage area of the DAS. Theremote units may transmit downlink signals to mobile phones or otherterminal devices within coverage areas serviced by the remote units oraccess points and may receive uplink signals from the terminal devices.Properties of the channels between the base stations and the head-endunits may be used to route the downlink signals to an appropriate accesspoint or base station. But, maintaining channel properties correspondingto the downlink signals may require knowledge of the connections betweenthe base stations and the telecommunication system during installationof the head-end units to manually identify the channels associated witheach port of the base stations.

SUMMARY

According to one aspect of the present disclosure, an identificationsystem may include an interface device and a processing device foridentifying channels on which signals are transmitted between a basestation and the interface device. The interface device may becommunicatively couplable to at least two ports of the base station toreceive downlink signals from the base station. The processing devicemay be couplable to the interface device. The processing device mayexecute instructions configured to cause the processing device toextract a first cell-specific reference signal from either (a) adownlink signal that does not have the embedded synchronization signalor (b) a downlink signal traversing the secondary channel. Theinstructions may also cause the processing device to generate a secondcell-specific reference signal using signal information from at leastone of the downlink signals. The instructions may also cause theprocessing device to determine a channel identification for one of theports of the base station by correlating the first cell-specificreference signal and the second cell-specific reference signal.

According to another aspect of the present disclosure, atelecommunication system may include a head-end unit communicativelycouplable to at least two ports of a base station to receive downlinksignals from the base station. The head-end unit may be configured toextract a first cell-specific reference signal from a downlink signal orsignals having the embedded synchronization signal. The head-end unitmay also be configured to generate a second cell-specific referencesignal using signal information from at least one of the downlinksignals. The head-end unit may also be configured to determine a channelidentification for one of the ports of the base station by correlatingthe first cell-specific reference signal and the second cell-specificreference signal.

According to another aspect of the present disclosure, a method mayinclude extracting a first cell-specific reference signal from one ofthe plurality of signals having an embedded synchronization signal. Themethod may also include generating a second cell-specific referencesignal using signal information from at least one of the plurality ofsignals. The method may also include determining a channelidentification for a port of a base station by correlating the firstcell-specific reference signal and the second cell-specific referencesignal.

The details of one or more aspects and examples are set forth in theaccompanying drawings and the description below. Other features andaspects will become apparent from the description, the drawings, and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of an environment for atelecommunication system that may include a channel identificationsystem according to one aspect of the present disclosure.

FIG. 2 is a block diagram of a channel identification system that may beincluded in a telecommunication system according to one aspect of thepresent disclosure.

FIG. 3 is a graphical mapping of downlink reference signals for a 2×2MIMO telecommunication system according to one aspect of the presentdisclosure.

FIG. 4 is a graphical mapping of downlink reference signals for a 4×4MIMO telecommunication system according to one aspect of the presentdisclosure.

FIG. 5 is a flow chart depicting an example of a process for using thechannel identification system of FIG. 2 to identify channel in a MIMOtelecommunication system according to one aspect of the presentdisclosure.

FIG. 6 is a graph simulation illustrating an example of a successfulcorrelation of cell-specific reference signal sequences according to oneaspect of the present disclosure.

FIG. 7 is a graph simulation illustrating an example of an unsuccessfulcorrelation of cell-specific reference signal sequences according to oneaspect of the present disclosure.

DETAILED DESCRIPTION

Certain aspects and features relate to a channel identification systemfor identifying multi-input, multi-output (“MIMO”) channels in atelecommunication system during installation and without knowledge ofthe respective MIMO channel properties. Each channel in thetelecommunication system may correspond to a port of a base stationcommunicatively coupled to the telecommunication station fortransmitting downlink signals from the base station to thetelecommunication system. In some aspects, the identity of each channelmay include a port number. A channel identification system may bepositioned in the telecommunication system to receive the downlinksignals and extract signal information for determining the identity ofeach channel transmitting the downlink signals from the base station. Insome aspects, the channels may include a primary channel and one or moresecondary channels between the ports of the base station and ports ofthe telecommunication system. The primary channel may include thechannel having a higher data rate than the other channels transmittingdownlink signals from the base station. Primary and secondarysynchronization signals may be embedded in one or more downlink signalsand transmitted from the base station on one or more of the channels.

The channel identification system may extract a cell-specific referencesignal sequence from a downlink signal that does not include an embeddedprimary and secondary synchronization signals, or, in instances where aprimary and secondary synchronization signals are transmitted onmultiple channels, the cell-specific reference signal sequence may beextracted from a downlink signal including synchronization signals andtraversing a secondary channel. In some aspects, the synchronizationsignals may include specific signal information to identify the portfrom which it was transmitted. The channel identification system maycorrelate the extracted cell-specific reference signal with a secondcell-specific reference signal generated from the signal informationfrom one of the downlink signals to determine whether the downlinksignals were transmitted from the same base station port.

In some aspects, the port number of a signal may be necessary tomaintain at least a portion of the MIMO channel properties to route thedownlink signals to an appropriate access point. The use of a channelidentification system according to some aspects, may increase efficiencyand ease in installing a telecommunication system by removing technicianlabor to predetermine the connections between the ports of a basestation and the telecommunication system. A channel identificationsystem according to some aspects may also increase efficiency of thetelecommunication system itself. Transmitting the downlink signals withthe MIMO channel properties may allow the use of multi-antenna spatialmultiplexing or beam-forming between a base station, or an eNB, and themobile devices or user equipment (“UE”) communicatively coupled to theaccess points. Multi-antenna spatial multiplexing and beam-forming mayallow the access points to achieve higher data capacity and bettercoverage in the telecommunication system.

Detailed descriptions of certain examples are discussed below. Theseillustrative examples are given to introduce the reader to the generalsubject matter discussed here and are not intended to limit the scope ofthe disclosed concepts. The following sections describe variousadditional aspects and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative examples but, like the illustrativeexamples, should not be used to limit the present disclosure. Thevarious figures described below depict examples of implementations forthe present disclosure, but should not be used to limit the presentdisclosure.

FIG. 1 shows a block diagram depicting an example of a telecommunicationsystem 100 that may include a channel identification system according toone aspect. The telecommunication system 100 may communicate signalsbetween a base station 102 in communication with the telecommunicationsystem 100 and terminal devices 104 a, 104 b located coverage areas 106a, 106 b, respectively, serviced by the telecommunication system 100.Non-limiting examples of a telecommunication system 100 may include aDAS or a repeater network. The terminal devices 104 a, 104 b located inthe coverage areas 106 a, 106 b serviced by the telecommunication system100 may include electronic devices (e.g., mobile devices) used tocommunicate voice or other data via the telecommunication system 100.

The telecommunication system 100 may communication signals to theterminal devices via a head-end unit 108 and one or more access points110 a, 110 b servicing the coverage areas 106 a, 106 b of thetelecommunication system 100 The head-end unit 108 may becommunicatively coupled to the base station 102 via any suitable manner.Communicatively coupling devices in a telecommunication system 100 caninvolve establishing, maintaining, or otherwise using a communicationlink (e.g., a cable, an optical fiber, a wireless link, etc.) tocommunicate information between the devices. The head-end unit 108 mayreceive downlink signals from a telecommunication provider network viathe base station 102 and may transmit uplink signals to thetelecommunication provider network via the base station 102. The accesspoints 110 a, 110 b may provide signal coverage in the coverage areas106 a, 106 b, respectively, served by the telecommunication system 100.In some aspects, the access points 110 a, 110 b may include transceivingdevice that may include or be communicatively coupled to one or moreports. A non-limiting example of an access point may include a remoteantenna unit. Providing signal coverage in the coverage area can includewirelessly transmitting downlink signals received from the head-end unit106 to terminal devices that are positioned in the coverage area.Providing signal coverage may also include wirelessly receiving uplinksignals from the terminal devices 104 a, 104 b positioned in therespective coverage areas 106 a, 106 b of the telecommunication system100. The access points 110 a, 110 b may transmit the uplink signals, ordata representing the uplink signals, such as packetized data generatedfrom received uplink signals, to the head-end unit 108.

The head-end unit 108 may include transmitter elements and receiverelements for communicating with the base station 102. In some examples,the head-end unit 108 may be configured for single input/single output(SISO) operation using a single transmitter element for transmittinguplink signals to the base station 102 and a single receiver element forreceiving downlink signals from the base station 102. In other examples,the head-end unit 108 may include multiple receiver elements andtransmitter elements to receive and transmit signals between the basestation 102 and the head-end unit 108. In such examples, the head-endunit 108 may be configured to operate in a multi-input/multi-output(MIMO) mode. FIG. 1 shows an example of the head-end unit 108 in a MIMOconfiguration. The base station 102 includes multiple ports 112 a-ncommunicatively coupled to multiple ports 114 a-n of the head-end unit108 to allow the head-end unit to operate in the MIMO configuration viachannels between the respective ports 112 a-n, 114 a-n. In some aspects,the ports 112 a-n, 114 a-n may be configured to transmit or receiveanalog signals (e.g., antenna ports). In additional and alternativeaspects, the ports 112 a-n, 114 a-n may be configured to receive digitalsignals (e.g., where the base station 102 includes a baseband unittransmitting digital signals).

For purposes of illustration, FIG. 1 depicts direct connections betweenthe base station and the telecommunication system 100 and between thehead-end unit 108 and the access points 110 a, 110 b in thetelecommunication system 100. But, the telecommunication system 100 mayuse any suitable implementation for communicatively coupling thedevices. In some examples, the head-end unit 108 may be communicativelycoupled to the access points 110 a, 110 b or base station 102, or both,via one or more active devices, including, but not limited to, extensionunits, switches, routers, or other intermediate devices. An activedevice may include a receiver for receiving a signal from one device inthe telecommunication system 100 and a transmitter for transmitting thereceived signal to another device in the telecommunication system 100.In additional or alternative aspects, the head-end unit 108 can becommunicatively coupled to the access points 110 a, 110 b or basestation 102, or both, via one or more passive interfaces, including, butnot limited to, a network cable or an air interface via which wirelesssignals can be communicated. Although the telecommunication system 100in FIG. 1 shows only one head-end unit 108 and two access points 110 a,110 b, a telecommunication system may include any number of head-endunits or access points without departing from the scope of the presentdisclosure. Also, the telecommunication system 100 may becommunicatively couplable to multiple base stations without departingfrom the scope of the present disclosure.

The telecommunication system 100 may include a channel identificationsystem 116 for identifying from which channel corresponding to ports 112a-n of the base station 102 downlink signals are received. In someaspects, the channel identification system 116 may be located in thehead-end unit 106 as shown in FIG. 1, although other placements for thechannel identification system 116 are possible without departing fromthe scope of the present disclosure.

FIG. 2 is a simple block diagram showing an example of the channelidentification system 116 that may be included in the telecommunicationsystem of FIG. 1. The channel identification system 116 includes aninterface device 200. The interface device may be a base transceiverstation (BTS) interface device for communicating or otherwiseinterfacing with a base station in a telecommunication (e.g., basestation 102 in FIG. 1). In some aspects, the interface device 200 mayinclude a donor card. In some aspects, the interface device 200 may becommunicatively coupled to the ports 114 a-n of the head-end unit 108 ofFIG. 1 to receive downlink signals from the base station 102 of FIG. 1via the channels. In additional and alternative aspects, the interfacedevice 200 may include one or more analog-to-digital converters fordigitizing the downlink signals received from the base station 102.

The channel identification system 116 may also include one or moreprocessing devices communicatively coupled to the interface device 200.In the example shown in FIG. 2, processing devices of the channelidentification system 116 may include a field programmable gate array(FPGA) 202 and a digital signal processor (DSP) 204 communicativelycoupled to the interface device 200. Although only two processingdevices are shown in the channel identification system 116 in FIG. 2,the channel identification system 116 may include any number ofprocessing devices for executing the channel identification systemfunctionalities described herein, including one. Similarly, although thefield programmable gate array 202 and the digital signal processor 204are shown, the processing devices of the channel identification system116 may include one or more additional or alternative processingdevices, including, but not limited to a microprocessor, anapplication-specific integrated circuit (ASIC), and state machines. Insome aspects, the digital signal processor 204 may include a boardconnected to the backplane of the head-end unit 108.

In some aspects, the field programmable gate array 202 may be configuredto perform synchronous capture of the downlink signals received from theinterface device 200. In additional and alternative aspects, the digitalsignal processor 204 may be configured to process the downlink signalscaptured by the field programmable gate array 202. In some aspects, thedigital signal processor 204 may include a measurement receiver 206 anda memory device 208 as shown in FIG. 2. The measurement receiver 206 maybe a receiver device configured to measure the characteristics of signalreceived from a base station communicatively coupled to thetelecommunication system in which the channel identification system 116is located (e.g., base station 102 in telecommunication system 100). Themeasurement receiver 206 may be communicatively coupled to the memorydevice 208. The memory device 208 may include any type of memory devicethat retains stored information when powered off. Non-limiting examplesof the memory device 208 may include electrically erasable andprogrammable read-only memory (EEPROM), flash memory, or any other typeof non-volatile memory. In some examples, at least a portion of thememory device 208 may include a medium from which the measurementreceiver 206 can read instructions 210 for carrying out one or morechannel identification functionalities. The instructions 210 may includeprocessor-specific instructions generated by a compiler or aninterpreter from code written in any suitable computer-programminglanguage, including, for example, C, C++, C#, etc.

In some examples, the instructions 210 may include the following generalequation for defining a cell-specific reference signal:

${{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots\mspace{14mu},{{2N_{RB}^{\max,{DL}}} - 1},$where n_(s) is a slot number within a radio frame and l is an orthogonalfrequency-division multiplexing (OFDM) symbol number within the slot. Insome aspects, the cell-specific reference signals may be a type of Goldsequence having sufficient auto-correlation properties in code divisionmultiple access (CDMA) applications. Cell-specific reference signals maybe a function of a slot number (n_(s)), an orthogonal frequency-divisionmultiplexing (“OFDM”) symbol number (l), a cell ID, and a cyclic prefixmode.

The cell-specific reference signals may be a type of Gold sequencehaving sufficient auto-correlation properties in code division multipleaccess (CDMA) applications. In some aspects, pseudo-random sequences maybe defined by a length-31 Gold sequence. The instructions 210 may alsoinclude the following general equations for defining an output sequencec(n) of length M_(PN), where n=0, 1, . . . , M_(PN)−1:c(n)=(x ₁(n+ _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2,where x₁ and x₂ represent block vectors from component PN generators andN_(c) is a constant equal to 1600. In some aspects, a first shiftregister may be initialized with all zeros and a second shift registermay be initialized at the start of each OFDM symbol with the followingrelationship that may be included in the instruction 210:c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID) ^(cell)+N _(CP),where N_(CP) represents the downlink cyclic prefix length that is equalto 1 for a normal cyclic cell prefix and 0 for an extended cyclicprefix, N_(ID) ^(cell) is the physical layer cell identity, and n_(s) isthe slot number within a radio frame.

In some aspects, the location of the downlink cell-specific referencesignals may be mapped for each port 112 a-n, 114 a-n transmitting orreceiving the signals, respectively, via the channels. FIGS. 3 and 4show examples of a graphical mapping of downlink cell-specific referencesignals corresponding to information that may be stored as instructions210. In FIG. 3, the cell-specific reference signals may be transmittedvia one or more channels and used to identify the remaining channels ina 2×2 MIMO telecommunication system. The map includes grids 300, 302representing a first port (e.g., port {0}) and a second port (e.g., port{1}), respectively. In some aspects, the grids 300, 302 may representtwo of the ports 114 a-n of the head-end unit 108 of FIG. 1. In otheraspects, the grids 300, 302 may represent or correspond to two of theports 112 a-n of the base station 102 of FIG. 1. Each grid 300, 302 mayinclude slots 304, each representing a resource element with afrequency-domain index time index (1) and a time-domain index (k). Aresource element may include the smallest time-frequency unit for adownlink transmission.

Grid 300 may include slots 306, a subset of the slots 304 having an R₀and indicating that a cell-specific reference signal is transmitting aresource element in the slot 304, 306. Similarly, grid 302 may includeslots 308, a second subset of the slots 304 having an R₁ and indicatingthat a cell-specific reference signal is transmitting a resource elementin the slot 304, 308. A downlink physical broadcasting channel (PBCH)may correspond to a set of resource elements carrying information to thechannel identification system 116. A third subset of slots 310 in thegrids 300, 302 indicate that a cell-specific reference signal istransmitting on the same slot number of another port in thetelecommunication system 100. In some aspects, resource elements usedfor transmission of cell-specific reference signals on any of the portsin a slot may not be used for any transmission on any other port in thesame slot and may be set to a value of zero. In some aspects, thecell-specific reference signals may be a function of a slot number(n_(s)), an orthogonal frequency-division multiplexing symbol number(l), a cell ID, and a cyclic prefix mode. The cell-specific referencesignals mapping to a resource element may be a function of the portnumber (p), the slot number (n_(s)), the symbol number (l) and thedownlink number of resource blocks (RBs).

FIG. 4 shows an example of a graphical mapping of downlink cell-specificreference signals for a 4×4 MIMO telecommunication system correspondingto information that may be stored as instructions 210. The map includesgrids 400, 402, 404, 406 representing a first port (e.g., port {0}), asecond port (e.g., port {1}), a third port (e.g., port {2}), and afourth port (e.g., port {3}) respectively. Grid 400 includes slots 408having an R₀ and indicating that a cell-specific reference signal istransmitting a resource element in the grid slot. Grid 402 includesslots 410 having an R₁ and indicating that a cell-specific referencesignal is transmitting a resource element in the grid slot. Grid 404includes slots 412 having an R₂ and indicating that a cell-specificreference signal is transmitting a resource element in the grid slot.Grid 406 includes slots 412 having an R₃ and indicating that acell-specific reference signal is transmitting a resource element in thegrid slot. The information graphically displayed in the maps of FIGS. 3and 4 may be usable by the channel identification system 116 of FIG. 1in extracting and generating cell-specific reference signals to identifythe channels of the base station 102 corresponding to the downlinksignals received by the interface device 200 of FIG. 2 from the ports112 a-n of the base station 102.

FIG. 5 is a flow chart illustrating an example of a process that may beimplemented to identify channels in a telecommunication system. Theprocess, described herein with reference to FIGS. 1 and 2, may beimplemented by the channel identification system 116 of FIG. 1 or by anyother suitable system or subsystem in a telecommunication system.

In block 500, the channel identification system 116 synchronouslycaptures analog signals transmitted by the base station 102 to thehead-end unit 108. In some aspects, downlink signals may be receivedfrom the ports 112 a-n of the base station 102 by the interface device200 of the channel identification system 116 via the channels betweenports 112 a-n and ports 114 a-n. The channels may include a primarychannel, or the channel having a higher data rate than other channels ofthe base station 102, and one or more secondary channels. The downlinksignals may be received at the ports 114 a-n of the head-end unit. Insome aspects, the ports 114 a-n may correspond to donor ports of theinterface device 200. In one example, the base station 102 may includetwo ports 112 a, 112 b communicatively coupled to two ports 114 a, 114 bof the head-end unit 108. In this example, the downlink signals fromport 112 a may be received at port 114 a and the downlink signals fromport 112 b may be received by port 114 b, or the downlink signals fromport 112 a may be received at port 114 b and the downlink signals fromport 112 b may be received by port 114 a.

In some aspects, the downlink signals may be converted from analog todigital. In some aspects, the downlink signals may be digitized by oneor more analog-to-digital converters of the interface device 200. Thesynchronous capture of the digitized downlink signals may includesampling the digitized downlink signals at the same time, i.e., a firstsample from a first digitized downlink signal and a second sample fromsecond digitized downlink signal may be associated with the samesampling time. In some examples, the synchronous capture may beperformed by the field programmable gate array 202 on a backplane of thehead-end unit 108. In some aspects, the captured samples of thedigitized downlink signals may be made available to the digital signalprocessor 204 and stored in the memory device 208.

In block 502, primary and secondary synchronization signals areidentified in the synchronously captured samples. In some aspects, thedownlink signals may be down-sampled (e.g., decimated by 16) tofacilitate the identification of the primary and secondarysynchronization signals. In some aspects, the primary and secondarysynchronization signals may be identified by the measurement receiver206. In further aspects, the measurement receiver 206 may retrieve thesamples from the memory device 208. In other aspects, the measurementreceiver 206 may retrieve the samples from the field programmable gatearray 202. The primary and secondary synchronization signals may betransmitted from one or more ports 112 a-n of the base station 102 assignals embed in the downlink signals transmitted to the head-end unit108. In some aspects, primary and secondary synchronization signals maybe embedded in only a downlink signal on a single channel (e.g., fromone of the ports 112 a-n). In other aspects, primary and secondarysynchronization signals may be embedded in the downlink signalstransmitted on multiple or all of the channels (e.g., from multiple orall of ports 112 a-n). The primary synchronization signal may be locatedin a specific OFDM symbol, slot, and sub-frame of a radio frame toenable synchronization of the head-end unit 108 or other equipment inthe telecommunication system 100. The secondary synchronization signalmay be located in the same sub-frame but in an OFDM symbol adjacent tothe primary synchronization signal to provide the channel identificationsystem 116 with a cell identifier corresponding to the channel, or port112 a-n, from which the signal was transmitted. The cell identifier mayenable the head-end unit 108 to determine whether the port 112 a-n ofthe base station 102 from which the primary synchronization signal andsecondary synchronization signal are transferred corresponds to theprimary channel.

In block 504, the broadcast channel (BCH) may be decoded for the digitalsignal sample(s) including the primary and secondary synchronizationsignals. In some aspects, decoding the broadcast channel may allow thechannel identification system 116 to determine a number of portstransmitting downlink signals from the base station 102 (e.g., 2 portsfor a 2×2 MIMO, 4 ports for a 4×4 MIMO, etc.). The broadcast channel mayalso provide bandwidth and frame information for the ports 112 a, 112 bof the base station. In some aspects, the broadcast channel may bedecoded using known techniques. In one example, the down-sampling may befrom 30.72e6 to 1.92e6 Hz since the broadcast channel may be centered at1.08e6 Hz. Time synchronization may be performed by the measurementreceiver 206 subsequent to the down-sampling by relocating the primaryand secondary synchronization signals in the down-sampled signals toidentify the frame boundaries and slot numbers. For symbols that containthe master information block (MIB) on the broadcast channel, the cyclicprefix may be removed. A fast Fourier transform (FFT) algorithm may beperformed for a conversion to the frequency domain for the resourceelements. Channel estimation and interpolation may be performed in thesub-frame using cell-specific reference signals. Channel correction maybe performed to the resource elements in the frequency domain and theresource elements carrying broadcast channel information may beextracted according to the number of ports. In some aspects, recoveryfrom the space-frequency block coding (SFBC), or, for a case of fourports, a combination of space-frequency block coding and frequencyswitched transmit diversity (FSTD) may be used. The resource elementsmay be demodulated and mapped to bit sequence. In some aspects,descrambling, rate de-matching, and Viterbi decoding may also beperformed. The cyclic redundancy check (CRC) generated from MIB payloadmay be checked and compared using an exclusive disjunction operation tozeroes having corresponding 16-bit mask. The master information blockinformation may be extracted. In some aspects, the master informationblock information may include a downlink bandwidth, physical hybrid-ARQindicator channel (PHICH) configuration, system frame number (SNF), anda number of ports.

In blocks 506 and 508, a cell-specific reference signal may beextracted. In block 506, the cell-specific reference signal may beextracted from a downlink signal that does not include the primary andsecondary synchronization signals based upon the primary and secondarysynchronization signals being embedded only in the downlink signals fromone port 112 a-n of the base station 102. For example, where there aretwo ports 112 a-n corresponding to a primary and secondary channel, thecell-specific reference signal may be included in downlink signalstraversing the primary channel or the secondary channel. Thecell-specific reference signal may be extracted from the primary channelbased upon the synchronization signals being included in downlinksignals traversing the secondary channel. The cell-specific referencesignal may be extracted from the secondary channel based upon thesynchronization signals being included in downlink signals traversingthe primary channel. In block 508, a cell-specific reference signal maybe extracted from a downlink signal traversing a secondary channel basedupon primary and secondary synchronization signals being embedded inboth primary and secondary channels.

In blocks 506 and 508, the cell-specific reference signal may beextracted by re-identifying the primary and secondary synchronizationsignals at a full sampling rate. A search of the primary and secondarysynchronization signals may be performed at full rate to achieve moreaccurate slot synchronization. In some aspects, measurement receiver 206may re-identify retrieved the digital downlink signal samples fromoriginal synchronous captures of the samples stored in the memory device208. In other aspects, the measurement receiver 206 may up-sample thepreviously down-sampled digital signal used to identify to the primaryand secondary synchronization signals as described in block 504. In someaspects, the result of the search may provide a frame boundary and aslot boundary for the digitized downlink signals. The measurementreceiver 206 may use this signal information to convert the samples fromthe time domain to the frequency domain to determine the cell-specificreference signal based on instruction 210 stored in the memory device208. In some aspects, the measurement receiver 206 may convert thesamples from the time domain to the frequency domain using a fastFourier transform (FFT) algorithm.

In block 510, a second cell-specific reference signal may be generatedfrom the digitized downlink signals. The second cell-specific referencesignal may be generated without using the information from the primaryand secondary synchronization signal. In some aspects, the secondcell-specific reference signal may serve as a hypothesis to the firstcell-specific reference signal. In some aspects, the secondcell-specific reference signal may be a Gold sequence and may bereconstructed using instructions 210 in the memory device 208. In someaspects, the second cell-specific reference signal may be generatedusing known values for the cell identifier, cyclic prefix, slot number,symbol number, and port number for the port 112 a-n from which thedownlink signal was transmitted. A fast Fourier transform (FFT)algorithm may be used to convert the information from the time domain tothe frequency domain to generate the cell-specific reference signalsfrom the downlink signals.

In block 512, the first cell-specific reference signal and the secondcell-specific reference signal may be correlated and compared todetermine a channel identification for the ports 112 a-n. A channelidentification may be verified where the two cell-specific referencesignal sequences are near-identical. In some aspects, the cell-specificreference signals may be compared based on the location of eachcell-specific reference signal and the relative strength of thecorrelation peak. When a strong correlation at lag zero is found withina given threshold, the hypothesis that the port 112 a-n corresponding tothe second cell-specific reference signal is from the same port 112 a-nas the port 112 a-n corresponding to the cell-specific reference signalmay be confirmed. In some aspects, the results are logged or otherwisestored in a database. In additional aspects, the channel identificationresults may be used to determine routing decisions for the downlinksignals to the access points. The channel identification results may bediscarded where the correlation and comparison is rejected.

In some aspects, the determination of which port 112 a-n of the basestation 102 or corresponding port 114 a-n of the head-end unit 108 maybe used by the channel identification system 116 to perform theautocorrelation functions for determining and verifying channelidentification may be based on the location of the primary and secondarysynchronization signals and, in some cases, the primary and secondarychannels identified by the channel identification system 116. In someaspects, a base station provider may locate synchronization signals onone or multiple ports. For example, in a 2×2 MIMO system,synchronization signals may be located on a first port only, on a secondport only, or on both a first and second port (e.g., ports 112 a, 112 bof the base station 102 of FIG. 1). The ports may be mapped to ports inthe telecommunication system (e.g., ports 114 a, 114 b of the head-endunit 108). The mapping of the ports 112 a, 112 b to ports 114 a, 114 bmay be direct (e.g., port 112 a to port 114 a, port 112 b to port 114 bas shown in FIG. 1) or may be inversed (e.g., port 112 a to port 114 b,port 112 b to port 114 a) to provide six potential scenarios fordetermining the ports used for correlation.

In a first scenario, the ports 112 a, 112 b may be directly connected toports 114 a, 114 b and the primary and secondary synchronization signalsmay be embedded in a downlink signal received at port 114 a. The directconnection informs that the synchronization signals were transmittedfrom port 112 a to port 114 a and port 112 b to port 114 b. Ports 112 a,114 a may be associated with the primary channel. The firstcell-specific reference signal may be extracted from the port associatedwith the non-primary channel, or secondary channel, (e.g., port 114 b).In this scenario, the second cell-specific reference signal may begenerated using information decoded from downlink signals received atport 114 a according to some aspects.

In a second scenario, the ports 112 a, 112 b may be reversely connectedto ports 114 a, 114 b and the primary and secondary synchronizationsignals may be embedded in a downlink signal received at port 114 b.Ports 112 a, 114 b may be associated with the primary channel. The firstcell-specific reference signal may be extracted from the port associatedwith the secondary channel (e.g., port 114 a). In this scenario, thesecond cell-specific reference signal may be generated using informationdecoded from downlink signals received at port 114 b.

In a third scenario, the ports 112 a, 112 b may be directly connected toports 114 a, 114 b and the primary and secondary synchronization signalsmay be embedded in downlink signals received at both ports 114 a, 114 b.Ports 112 a, 114 a may be associated with the primary channel. The firstcell-specific reference signal may be extracted from the port associatedwith the secondary channel (e.g., port 114 b). In this scenario, thesecond cell-specific reference signal may be generated using informationdecoded from downlink signals received at port 114 a.

In a fourth scenario, a reverse scenario of the third scenario, theports 112 a, 112 b may be reversely connected to ports 114 a, 114 b andthe primary and secondary synchronization signals may be embedded indownlink signals received at both ports 114 a, 114 b. The reverseconnection informs that the synchronization signals were transmittedfrom port 112 a to port 114 b and from port 112 b to port 114 a. Ports112 a, 114 b may be associated with the primary channel. The firstcell-specific reference signal may be extracted from the port associatedwith the secondary channel (e.g., port 114 a). In this scenario, thesecond cell-specific reference signal may be generated using informationdecoded from downlink signals received at port 114 b.

In a fifth scenario, the ports 112 a, 112 b may be directly connected toports 114 a, 114 b and the primary and secondary synchronization signalsmay be embedded in a downlink signal received at port 114 b. Ports 112a, 114 a may be associated with the primary channel. The firstcell-specific reference signal may be extracted from the port associatedwith the primary channel (e.g., port 114 a). In this scenario, thesecond cell-specific reference signal may be generated using informationdecoded from downlink signals received at port 114 b.

In a sixth scenario, the ports 112 a, 112 b may be reversely connectedto ports 114 a, 114 b and the primary and secondary synchronizationsignals may be embedded in a downlink signal received at port 114 a.Ports 112 a, 114 b may be associated with the primary channel. The firstcell-specific reference signal may be extracted from the port associatedwith the primary channel (e.g., port 114 b). In this scenario, thesecond cell-specific reference signal may be generated using informationdecoded from downlink signals received at port 114 a.

Although a 2×2 MIMO system is described, the methods for determining theports 112 a-n, 114 a-n for correlation of the cell-specific referencesignals may be applied to 4×4 MIMO systems with additional scenarios.Similarly, although the six scenarios describe specific ports 112 a-b,114 a-b and associated channels for correlation in a 2×2 MIMO system,downlink signals from various combinations of ports 112 a-b, 114 a-b maybe used for correlation without departing from the scope of the presentdisclosures.

In some aspects, a correlation as described in block 510 of FIG. 5 maybe graphically represented. For example, MATLAB scripts may be used toanalyze correlation of the first and second cell-specific referencesignals. FIGS. 6 and 7 include graphs illustrating examples of simulatedresults of the correlation and comparison of the cell-specific referencesignal sequences in a 2×2 MIMO system.

In FIG. 6, graph 600 represents a successful correlation of the firstand second cell-specific reference signals. The x-axis may representoffset or lag and the y-axis may represent an absolute value. In thisexample, six resource blocks of the cell-specific reference signals areused in the simulation. But, in some aspects, decoding the broadcastchannel prior to correlation may provide signal information such asbandwidth information that may allow for longer sequences. The peak 602may represent a match between the first and second cell-specificreference signals, indicating a strong correlation at the zero lag(e.g., twelve) of the correlation.

FIG. 7 shows a graph 700 indicating an unsuccessful correlation. Thecorrelation may be the equivalent to correlating a known cell-specificreference signal Gold sequence with random noise.

The foregoing description of the examples, including illustratedexamples, has been presented only for the purpose of illustration anddescription and is not intended to be exhaustive or to limit the subjectmatter to the precise forms disclosed. Numerous modifications,adaptations, and uses thereof will be apparent to those skilled in theart without departing from the scope of this disclosure. Theillustrative examples described above are given to introduce the readerto the general subject matter discussed here and are not intended tolimit the scope of the disclosed concepts.

What is claimed is:
 1. A channel identification system for a MIMOtelecommunication system wirelessly communicating with terminal devices,comprising: an interface device configured to receive downlink signalson channels corresponding to a first port and a second port of a basestation; and a processing device, wherein the processing device isconfigured to: synchronously capture samples of the downlink signalsreceived from the base station; determine a first cell-specificreference signal and a second cell-specific reference signal based onthe samples; and determine a channel identification corresponding to atleast one channel of the channels by correlating the first cell-specificreference signal and the second cell-specific reference signal.
 2. Thechannel identification system of claim 1, wherein the processing deviceis further configured to: decode a broadcast channel for a signal of thedownlink signals having an embedded synchronization signal.
 3. Thechannel identification system of claim 1, wherein the firstcell-specific reference signal is determined from one of: (a) a firstdownlink signal of the downlink signals that does not include anembedded synchronization signal or (b) a second downlink signal of thedownlink signals that includes the embedded synchronization signal andis associated with a secondary channel of the channels.
 4. The channelidentification system of claim 1, wherein the processing device isfurther configured to determine the first cell-specific reference signalusing a cell identifier, a cyclic prefix, a slot number, a symbolnumber, or a port number corresponding to a sample of a first downlinksignal of the downlink signals or a second downlink signal of thedownlink signals.
 5. The channel identification system of claim 1,further including a memory device configured to store the samples of thedownlink signals useable by the processing device to determine thesecond cell-specific reference signal.
 6. The channel identificationsystem of claim 1, wherein the processing device is configured todetermine the second cell-specific reference signal using a cellidentifier, a cyclic prefix, a slot number, a symbol number, or a portnumber corresponding to a stored sample of at least one of the downlinksignals.
 7. The channel identification system of claim 1, wherein theprocessing device further comprises at least a measurement receiverconfigured to receive the samples of the downlink signals received fromthe base station and to identify a primary synchronization signal and asecondary synchronization signal embedded in at least one of thedownlink signals.
 8. The channel identification system of claim 1,wherein the processing device is disposed in a head-end unit of the MIMOtelecommunication system.
 9. The channel identification system of claim1, wherein the processing device comprises at least a field-programmablegate array.
 10. A MIMO telecommunication system, comprising: a head-endunit communicatively couplable to a first port and a second port of abase station for receiving downlink signals via channels correspondingto the first port and the second port, the head-end unit beingconfigured to: receive, using an interface device in the head-end unit,the downlink signals and generate digital samples of the downlinksignals; synchronously capture the digital samples of the downlinksignals; determine a first cell-specific reference signal and a secondcell-specific reference signal based on at least one of the downlinksignals; and determine a channel identification corresponding to atleast one channel of the channels by correlating the first cell-specificreference signal and the second cell-specific reference signal.
 11. TheMIMO telecommunication system of claim 10, wherein the head-end unit isfurther configured to: identify one or more synchronization signalsembedded in at least one of the downlink signals; and decode a broadcastchannel for at least one of the downlink signals having one of the oneor more embedded synchronization signals, to determine a total number ofports transmitting the downlink signals.
 12. The MIMO telecommunicationsystem of claim 10, wherein the head-end unit comprises two ports in theMIMO telecommunication system to receive the downlink signals from twobase station ports.
 13. The MIMO telecommunication system of claim 10,wherein the head-end unit comprises four ports in the MIMOtelecommunication system to receive the downlink signals from four basestation ports.
 14. The MIMO telecommunication system of claim 10,wherein the head-end unit comprises: a processing device; and a memorydevice having instructions executable by the processing device forcausing the processing device to determine the first cell-specificreference signal using a cell identifier, a cyclic prefix, a slotnumber, a symbol number, or a port number corresponding to a digitalsample of a first downlink signal of the downlink signals or a seconddownlink signal of the downlink signals.
 15. The MIMO telecommunicationsystem of claim 10, wherein the head-end unit comprises: a processingdevice; and a memory device having instructions executable by theprocessing device for causing the processing device to determine thesecond cell-specific reference signal using a cell identifier, a cyclicprefix, a slot number, a symbol number, or a port number correspondingto a stored digital sample of at least one of the downlink signals. 16.The MIMO telecommunication system of claim 10, wherein the firstcell-specific reference signal is determined from one of: (a) a firstdownlink signal of the downlink signals that does not include anembedded synchronization signal or (b) a second downlink signal of thedownlink signals that includes the embedded synchronization signal andis associated with a secondary channel of the channels.
 17. The MIMOtelecommunication system of claim 10, wherein the head-end unit iscommunicatively coupled to one or more access points, each access pointbeing configured to receive the downlink signals and channel propertiesof the base station corresponding to the channel identification.
 18. Amethod, wherein the method is performed by a MIMO telecommunicationsystem wirelessly communicating with terminal devices, the methodcomprising: receiving a plurality of signals from ports of a basestation, the ports corresponding to at least a primary channel and asecondary channel; synchronously capturing digital samples of theplurality of signals; and determining a first cell-specific referencesignal and a second cell-specific reference signal based on the digitalsamples; and determining a channel identification corresponding to aport of the base station by correlating the first cell-specificreference signal and the second cell-specific reference signal.
 19. Themethod of claim 18, further including: decoding a broadcast channelbased on a location of an embedded synchronization signal in theplurality of signals.
 20. The method of claim 18, wherein determiningthe second cell-specific reference signal comprises using a cellidentifier, a cyclic prefix, a slot number, a symbol number, or a portnumber corresponding to a stored digital sample of one of the pluralityof signals.
 21. The method of claim 18, wherein the first cell-specificreference signal is determined from one of: (a) a first downlink signalof the plurality of signals that does not include an embeddedsynchronization signal or (b) a second downlink signal of the pluralityof signals that includes the embedded synchronization signal and isassociated with the secondary channel.
 22. The method of claim 21,further including: identifying one or more primary or secondarysynchronization signals subsequent to down-sampling the plurality ofsignals; and re-identifying the one or more primary or secondarysynchronization signals in a stored digital sample of the first downlinksignal or the second downlink signal at a full sampling rate.